Google covers best practices for expanding your site to new languages or country-based language variations. We discuss use cases of international sites, implementation of rel=”alternate” hreflang, and best practices.
Webmaster Help Center article on rel=”alternate” hreflang and hreflang=”x-default”:
https://support.google.com/webmasters/answer/189077
Working with multilingual sites:
http://googlewebmastercentral.blogspot.com/2010/03/working-with-multilingual-websites.html
Working with multiregional sites:
http://googlewebmastercentral.blogspot.com/2010/03/working-with-multi-regional-websites.html
New markup for multilingual content:
http://googlewebmastercentral.blogspot.com/2011/12/new-markup-for-multilingual-content.html
Introducing “x-default hreflang” for international landing pages:
http://googlewebmastercentral.blogspot.com/2013/04/x-default-hreflang-for-international-pages.html
Webmaster discussion forum FAQ on internationalization:
https://sites.google.com/site/webmasterhelpforum/en/faq-internationalisation
Webmaster discussion forum for internationalization:
http://productforums.google.com/forum/#!categories/webmasters/internationalization
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